The BACE1 (Beta-site Amyloid Precursor Protein Cleaving Enzyme 1) inhibitor, N-[3-((4aS,5R,7aS)-2-amino-5-methyl-4a,5,7,7a-tetrahydro-4H-furo[3,4-d] [1,3]thiazin-7a-yl)-4-fluorophenyl]-5-difluoromethylpyrazine-2-carboxamide, is a compound having the structure represented by formula (1) (to be simply referred to as “Pharmacological Compound 1”).

Pharmacological Compound 1 or a pharmaceutically acceptable salt thereof is expected to be used as a therapeutic agent for dementia and MCI (mild cognitive impairment) (Patent Document 1).